Separation and Purification

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Separation and Purification
In the next 3 classes we will study analytical
separations and extractions. This is a dynamic
and important field that has important
technological ramifications for todays society
Read Chapter 23-1
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(No Transcript)
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Simple Separations - Chapter 23
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Key Questions
What determines the relative amounts of a
molecule in each of the two phases? What
equations can we use to determine the
concentrations?
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We can use equilibrium thermodynamics to
determine the ratios of activities using the
below formula.
K is called a partition coefficient.
To solve for Si we will use mass balance
equations.
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We can also define as like we did before.
Remove concentration dependence with the
substitution
The book calls this q (23-2).
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Extraction
Here CV is the initial number of moles of S.
V1S1 is the number of moles in phase 1. V2S2
is the number of moles in phase 2.
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Assume phase 1 is an aqueous phase and phase 2
the nonpolar phase. Assume S is a nonpolar
molecule so it prefers phase 2. Lets say that
K3. Which is a better way to decrease the moles
of S in phase 1? Should I carry out one
separation where V13V2 or should I consider 2
sequential separations with V1V2?
In the latter scenario, after equilibrium, phase
one is separated from phase 2 and then phase one
is remixed with new phase 2.
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Assume phase 2 on top is non polar and phase 1 is
polar.
Equil.
Assume V1V2
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Assume phase 2 on top is non polar and phase 1 is
polar.
Equil.
Equil.
Assume V13V2
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Assume phase 1 is an aqueous phase and phase 2
the nonpolar phase. Assume S is a nonpolar
molecule so it prefers phase 2. Lets say that
K3. Which is a better way to decrease the moles
of S in phase 1? Should I carry out one
separation where 16V1V2 or should I consider 4
sequential separations with V1V2?
In the latter scenario, after equilibrium, phase
one is separated from phase 2 and then phase one
is remixed with new phase 2.
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Assume phase 1 is an aqueous phase and phase 2
the nonpolar phase. Assume S is a nonpolar
molecule so it prefers phase 2. Lets say that
K4. Which is a better way to decrease the moles
of S in phase 1? Should I carry out one
separation where 32V1V2 or should I consider 3
sequential separations with V1V2?
versus
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More Complex Separations
We will now extend what we have just studied, in
order to include acid-base chemistry in the
aqueous phase
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Lets not worry about reactions in red box.
V1
V2
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You will treat a problem like this for your
homework.
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Here are the extraction equations developed in
class for The NH3/NH4 problem discussed in class.
If V1V2 then
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Final Comments

• A quantitative analysis of extractions and
  separations is similar to that of all previous
  equilibria that we have studied.
• One solves for concentrations as before by
  writing down equilibrium expressions along with
  MB and CB equations in order to find a master
  equation which is a function of just one
  concentration.
• The two new features of separation and extraction
  are (1) the concept of equilibria between two
  species in different phases and (2) the need to
  write mass balance in terms of moles instead of
  concentration.